This invention relates generally to roof truss construction and more particularly provides a displaced diagonal web system for a bowstring type roof truss which facilitates the inclusion of an unobstructed floor system at the bottom chord.
The considerable space defined between the top and bottom chords of a long span roof truss system is generally wasted due to interference with passage occasioned by the diagonal webs. It may be highly desirable to convert such wasted space to usable space by framing a floor system directly into the bottom chord. However, to provide unrestricted walk-through access between bays, the bottom intersection point of the diagonal web members must be raised to a location displaced substantially upward from the bottom chord and approaching a position midway between the top and bottom chords which is at shoulder height or thereabout.
In considering steel truss systems, one may totally eliminate the diagonals, replacing their function with welded continuity of massive vertical elements. This type of truss is generally termed a "Vierendeel" truss system. The problem of vertical plane bending in both the webs and the chords is experienced. The "Vierendeel" type truss system can be defined as an untriangulated perpendicular lacing between compression and tension chords in a structural system for resisting load components perpendicular to the longitudinal axis in which composite rigidity is accomplished by bending strength continuity between the chords and the connecting webs rather than additional diagonal members to the joints.
On a practical basis, in using wood one cannot achieve joint continuity sufficient to create a reliable Vierendeel bending continuity between the top and bottom chords. Even in steel framing the Vierendeel truss has limited practical use because of high cost. Elimination of diagonals necessitates supplanting normal truss action with more costly bending in either or both top and bottom chords.